Everyone agrees that the GT-R is pretty substantially under-rated. I have not kept track carefully since the initial launch of the car but in that year most folks in the know agree that the car is probably putting out much closer to 530 hp opposed to the spec. of 480. The cars advanced ATTESA-ETS (traction control), AWD system and launch control contribute as well.

Insideline test results suggest that Nissan's claims are accurate. They used a Mustang AWD dyno. 91 octane was used in second test. See below: